1. Field of the Invention
The present invention relates to a method and an apparatus for liquid preparation of a photographic reagent, and more specifically, to a liquid preparation method for a silver halide emulsion for use in a heat-developable photosensitive material.
2. Description of the Related Art
The photosensitive material is classified broadly into the silver halide photographic sensitive material which uses a gelatin-based binder and the heat-developable photosensitive material which uses a polymer latex-based binder such as an SBR (styrene-butadiene copolymer)-based binder, either photosensitive material using a silver halide emulsion.
A heat-developable photosensitive material which contains an organic silver salt, a reducing agent for silver ion, a polymer latex, and a photosensitive silver halide emulsion, and the like is used as a coating liquid for use in image formation. In this case, the coating liquid is prepared by adding a small amount of the silver halide emulsion to a mother coating liquid containing the organic silver salt, the reducing agent for silver ion, the polymer latex, and the like.
On the other hand, as for the silver halide photographic material, a large amount of the silver halide emulsion is consumed, and accordingly the liquid preparation of the silver halide emulsion has been made with the so-called system line for continuous liquid preparation, as disclosed in Japanese Patent Application Publication No. 47-30315, in which the silver halide emulsion is continuously melted in a heating tank heated by a heating device and a required amount is continuously taken out and measured.
Generally, the liquid preparation operations in the production of the silver halide emulsion include a process for preparing silver halide grains and a process of adding a sensitizing dye. The preparation of silver halide grains is made by a liquid preparation method in which a solution of a water soluble silver salt and a solution of a water soluble halide are mixed together and allowed to react with each other, and there have been used such mixing reactors for reaction by mixing as described in Japanese Patent Application Publication No. 51-83097, U.S. Pat. No. 3,785,777, Japanese Patent Application Publication No. 60-117834, Japanese Patent Application Publication No. 57-92524, and Japanese Patent Application Publication No. 48-21045. The addition of the sensitizing dye is made subsequently to the preparation of silver halide grains.
In the case of the heat-developable photosensitive material, however, the used amount of the silver halide emulsion is extremely smaller as compared with the silver halide photographic material, and hence there is a drawback that the quality deterioration occurs in the prepared liquid remaining in the heating tank with elapse of the time (hereafter referred to as “time elapse in melt”) when the conventional liquid preparation method is applied in which the silver halide emulsion is melted continuously in the heating tank heated by the heating device and the amount required for liquid preparation is continuously measured and taken out from the tank. When the used amount is small, there is a problem that the quality deterioration and the reagent loss are enhanced due to the residuals in the conduit pipe in the system line for continuous liquid preparation. Furthermore, the sensitizing dye used in the heat-developable photosensitive material is required to avoid mutual contamination of different kinds of dyes, but it is the case in a conventional liquid preparation apparatus that no equipment is arranged for preventing the mutual contamination. As for the problems of the time elapse in melt, reagent loss and mutual contamination, they are not restricted to the liquid preparation of the silver halide emulsion, but similar troubles occur when the liquid preparation involves a photographic reagent small in its amount used.
On the other hand, as for the silver halide grains in the production of the silver halide emulsion, the diameters of silver halide grains are preferably to be made small, and particularly, in the case of the silver halide emulsion for use in the heat-developable photosensitive material, it is essential to make the grain diameter small and to make the distribution width of the grain diameter narrow for the purpose of suppressing the white turbidity occurring after image formation. In this connection, however, there is a problem that neither satisfactory grain diameters nor a satisfactory distribution width of grain diameter can be obtained by simply using the above-described conventional mixing reactor as it is.
In the process for producing the silver halide emulsion, not only a single kind of emulsion is produced but also different emulsions added with other kinds of sensitizing dyes are produced, and accordingly the contamination of the sensitizing dye occurs if the sensitizing dye used in the last production operation is insufficiently removed at the time of lot renewal, leading to a production failure. In particular, when the sensitizing dye used in the production of the silver halide emulsion for use in the heat-developable photosensitive material contaminates other emulsions, such serious production failures as adverse generation of fog and the like are caused, and hence sufficient removal of the dye is required. Conventionally, the removal of the sensitizing dye remaining in the apparatus in the process is made by warm-water rinsing, acid-solution rinsing, alkali-solution rinsing, and combinations thereof, where there is a problem of persisting silver grains when some portions of the physical objects to be rinsed get away from the rinsing liquids. In addition, there is also a problem that a dedicated equipment is required for disposing the rinsing liquid wastes and the running cost is increased.